Gas discharge device with glow discharge igniting structure

ABSTRACT

The invention relates to a device including a gas and/or vapour discharge lamp. This lamp comprises a discharge tube which is enclosed in an outer envelope. According to the invention a glow discharge is first produced in the space between the outer envelope and the discharge tube to bring the lamp into operation. An advantage thereof is that the required ignition voltage for initiating the discharge in the discharge tube may be comparatively small.

United States Patent 1 BEST AVAILABLE cm de Vrijer [451 July 15, 1975 [54] GAS DISCHARGE DEVICE WITH GLOW 2,291,952 8/1942 Dench 313/25 X RE 3,363,134 1/1968 Johnson 313/225 X DISCHARGE IGNITIN? STRUCTI? 3,484,637 12/1969 VanBoort et al. 313/229 X Inventor: Berth-s de J smge 3,609,437 9/1971 To] et al. 313/184 x Eindhoven, Netherlands [73] Assignee: U.S. Philips Corporation, New primary Examiner pa|mer C Demeo York, Attorney, Agent, or Firm-Frank R. Trifari; George B. 22 Filed: 0a. 25, 1972 Berka [2]] Appl. No.: 300,746

Related US. Application Data TRACT [63] g of March 1969 The invention relates to a device including a gas anda an one /or vapour discharge lamp. This lamp comprises a dis- [52] U S Cl 313/25 3l3/186 313/201, charge tube which is enclosed in an outer envelope.

I I I u 315/66 According to the invention a glow discharge is first 51 1m. 01. H01 j 61/54 Produced in the space between the Outer n p and [58] Field of Search 313/25, 26, 184, 185, 187, the discharge tube to bring the lamp into Operation- 313/201, 225, 228, 186; 315/60 An advantage thereof is that the required ignition voltage for initiating the discharge in the discharge 5 References Ci d tube may be comparatively small.

UNITED STATES PATENTS 6 Claims, 2 Drawing Figures 2,273,450 2/1942 Rentschler 313/225 X 4 Q ain GAS DISCHARGE DEVICE WITH GLOW DISCHARGE IGNITING STRUCTURE electrode being provided at either end of the discharge tube, which is enclosed in an outer envelope, and in which at least partially bare current conductors are provided between the outer envelope and the discharge tube, a gas being present in the space between the outer envelope and the discharge tube, the voltage between the bare parts of the current conductors located in the outer envelope but outside the discharge tube being lower in the operating condition of the dischargetube than the voltage which is required to maintain a dis.- charge between said bare parts. Furthermore the invention relates to a lamp which is particularly suitable for such a device.

In the preamble a current conductor which is at least partially bare is to be understood to mean a current conductor which is free from electrical insulation at at least one area.

An advantage of a device of the kind described in the preamble is the high specific luminous flux of the discharge lamp used therein. A drawback is, however, that the ignition voltage for introducing a discharge between the internal electrodes of this lamp is rather high.

It is an object of the invention to reduce the ignition voltage in a simple manner.

A device according to the invention including a gas and/or vapour discharge lamp comprising a discharge tube having a wall poorly conducting electricity, an internal electrode being provided at either end of the discharge tube, which is enclosed in an outer envelope and in which at least partially bare current conductors are provided between the outer envelope and the discharge tube, a gas being present in the space between the outer envelope and the discharge tube, the voltage between the bare parts of the current conductors located in the outer envelope but outside the discharge tube being lower in the operating condition of the discharge tube than the voltage which is required to maintain a discharge between said bare parts is characterized in that the pressure of the gas between the outer envelope and the discharge tube is between Torr and 1 Torr, and that the voltage between the bare parts of the current conductors is higher than the voltage which is required for igniting a glow discharge between said bare parts of the current conductors when the device is switched on, but the discharge tube is not yet ignited, and that only in the situation whereby a discharge, outside the tube, between said bare parts of the current conductors is ignited the voltage across the internal electrodes is sufficient to ignite the discharge in the discharge tube.

An advantage of a device according to the invention is that the required ignition voltage across the internal electrodes of the discharge tube may now be comparatively low. The pressure of the gas between the outer envelope and the discharge tube is chosen to be such that a glow discharge may arise in the outer envelope.

The discharge lamp in adevice according to the invention is ignited in a completely novelwmannenBy at least partially ionizing the gasbetween the outer envelope and the dischargetube, thus by making it conductive, an external electrically conducting strip is simulated, as it were, on the wall of the discharge tube. As already previously noted this wallconsists of a material which poorly conducts electricity. The ignition voltage of the discharge lamp is now reduced with the aid of the simulated strip.

It is to be noted that it is known per se to fill the outer envelope of a discharge tube with a gas at a comparatively low pressure (see, for example, Dutch Patent Specification 41741). In known devices it was, however, ensured that no discharge could occur between bare conductors in the outer envelope. The gas in the outer envelope was sometimes used to inhibit oxidation of metal parts in the outer envelope.

In a device according to the invention the at least partially bare current conductors between the outer envelope and the'discharge tube may, for example, be incorporated in an electric circuit which is entirely separate from the supply circuit of the internal electrodes of the discharge tube.

The device is constructed in, for example, such a manner that when the discharge tube is ignited the volt age set up across the bare current conductors is re duced by means of relays or, for example, Zener diodes to so low a voltage that no discharge occurs any longer in the outer envelope.

In a device according to the invention at least one of the at least partially bare current conductors is preferably electrically connected to one of the internal electrodes.

An advantage of this preferred solution is that the circuit may becomes simpler because now, for example, the internal electrodes and the bare current conductors may be supplied form the same current source.

The electrical connection referred to in the lastmentioned preferred solution may be provided, for example, either partly outside the outer envelope, for example, in a lamp cap or entirely within the outer envelope. If this electrical connection is located within the outer envelope an additional advantage is obtained because the number of electrical lead-in wires through the wall of the outer envelope can thus be small.

It is feasible that not only one bare current conductor is connected to an internal electrode of the discharge tube, but that also a further bare current conductor in the outer envelope is connected to a further (second) internal electrode. If in the latter case the electrical connections of the bare current conductors to the internal electrodes are located within the outer envelope the number of electrical lead-in wires through the wall of the outer envelope may even be reduced to two.

The gas between the outer envelope and the discharge tube may be, for example, nitrogen or a different gas.

The gas between the outer envelope and the discharge tube is preferably a noble gas.

An advantage of a noble gas-filling of the outer envelope is that there is no risk of the components within the outer envelope being attached.

It is feasible that the discharge lamp suitable for a device according to the invention is a low-pressure lamp.

The discharge lamp is preferably a high-pressure lamp. A high-pressure lamp is to be understood to mean a lamp having a discharge tube in which the pressure is at least 20 Torr. Particularly in high-pressure lamps the proposed manner of ignition by means of an auxiliarly discharge in the outer envelope is useful because the ignition voltage of high-pressure lamps is mostly rather high.

' The discharge lamp may be, for'example, a mercury lamp.

.The discharge lamp is preferably a high-pressure sodium vapour discharge lamp in which the wall of the discharge tube poorly conducting electricity consists of a densely sintered aluminium oxide'and in which the gas between the outer envelope and the discharge tube is a noble gas.

This combination has the advantage that both a high specific luminous flux may be accompanied by a comparatively low ignition voltage and that there is no risk of the wall of the discharge tube being attached.

In an advantageous embodiment of the lastmentioned preferred solution the noble gas between the outer envelope and the discharge tube is argon at a pressure of between Torr and 10 Torr.

An advantage of this preferred solution is that the ignition voltage may be reduced to less than 70 of the ignition voltage which would be required if vacuum excists in the outer envelope.

ln afurther advantageous embodiment of a lamp according to the invention in which at least one of the internal electrodes is electrically connected to an at least partially bare current conductor in the outer envelope and in which this electrical connection is located within the lamp, the said electrical connection includes an impedance which does not form part of the main current circuit of the internal electrodes of the discharge tube, and in which both this electrical connection and the impedance forming part thereof and the main current supply conductor of the internal electrode, which is connected to the impedance, are electrically insulated from the gas in the outer envelope.

An advantage of this preferred solution is that the intensity of the discharge in the outer envelope may thus be reduced in a simple manner so that possible damage to the internal part of the lamp as a result of the discharge in the outer envelope is substantially excluded.

In a further advantageous embodiment of a lamp suitable for a device according to the invention the bare parts of the current conductors between the outer envelope and the discharge tube are provided with an emitter.

' An emitter is to be understood to mean a substance reducing the ignition voltage.

An advantage of this solution is that a glow discharge may arise in the outer envelope already at comparatively very low voltages across the bare current conductors,'which glow discharge may initiate the main discharge in the discharge tube.

In order that the invention may be readily carried into effect, a few embodiments thereof will now be described in detail by way of example with reference to the accompanying diagrammatic drawing, in which:

FIG. 1 is a cross-sectional, partly elevational view of an electric gas discharge lamp according to the invention;

FIG. 2 is a cross-sectional, partly elevational view of a second electric discharge lamp according to the invention.

In FIG. 1 the envelope of a discharge space 2 is indicated by 1, in which space a discharge may be produced in an atmosphere which, for example, consists of sodium vapour, mercury vapour and a noble gas, for

example, xenon. The envelope 1 consists of transparent densely sintered aluminium oxide. The electrodes 3 and 4 which are formed in known manner and include, inter alia, a tungsten filament are providedat the ends of the discharge space 2. The electrodes 3 and 4 are secured to current supply members 5 and 6 which consist of niobium tubes. Two sealing members which likewise consist of transparent densely sintered aluminium oxide are indicated by 7 and 8; they are secured in the envelope 1 by means of sintering. Two covers are indicated by 9 and 10 which likewise consist of densely sintered transparent aluminium oxide and which are secured both to the envelope 1 and to the sealing membets 7 and 8 and to the lead-throughs 5 and 6. The discharge tube 1 is arranged within an outer envelope 11 which consists, for example, of hard glass. This outer envelope has a pinch 12 in which two supporting wires 13 and 14 are secured which also serve as current supply conductors for the electrode 4 and the electrode 3, respectively. Two strip-like connection members are indicated by 15 and 16, which connect the electrodes 3 and 4 to the supporting wires 14 and 13, respectively.

In the (high pressure sodium) lamp described supply wire 13 and the strip 16 connected thereto form a bare current conductor. This also applies to the current supply wire 14 and the strip 15. Argon gas at a pressure of 5.10 Torr is provided between the outer envelope l1 and the discharge tube 1. The distance between the strips 15 and 16 is approximately l2 cms, the lamp is suitable for 400 Watt. The ignition voltage is 750 volts in the case of the lamp described. However, if the space between the outer envelope and the discharge tube was not provided with gas, but with vacuum (consequently this is not a lamp according to the invention) the ignition voltage was 1,600 volts. The latter value is considerably higher than the previously mentioned voltage of 750 Volts which is required for the ignition of the described lamp according to the invention.

In the described lamp according to the invention a glow discharge is first produced in the outer envelope after switching on. This glow discharge gives rise to the considerably lower ignition voltage of this lamp.

In FIG. 2 a discharge tube is indicated by 1 which is exactly equal to the discharge tube indicated by l in FIG. 1. An outer envelope is indicated by 11'; 15 and 16' indicate connection strips for the current supply to the electrodes 3' and 4, respectively (the strips are connected to supply conductors l4 and 13'). In FIG. 2 the strip 15 has an extended portion 25 provided with an electrically insulated resistor 26 and a bare conductor 27 which is provided with an emitter. The strip 16' has an additional portion 28 including an electrically insulating resistor 29 and a bare conductor 30. The conductor 30 is provided with an emitter. Unlike the lamp of FIG. 1 only the parts 27 and 30 in FIG. 2 are bare current conductor parts between the outer envelope 11 and the discharge tube 1. This means that the parts 13, 14, 15', 16, 25 and 28 and the parts of the tube 5 and 6 exposed to the gas atmosphere in the outer envelope are surrounded by an insulation layer. The insulation of conductor 14' is indicated by 17 In FIG. 2 argon gas at a pressure of 5.10 Torr is provided between the outer envelope l1 and the discharge tube :1. Alsoin 'FIG. 2 theignition voltage of the lamp is lower than the voltage which would be required for-ignition a corresponding lamp having vacuum filledouter envelope The present invention is in no way limited to discharge lamps for general illumination purpose. In fact, it is feasible that the invention is also'applicable to the ignition of a discharge flash-light lamp which is mounted in an outer envelope.

What is claimed is:

l. A gas discharge device comprising a main discharge tube having a tubular wall of a material that is a poor conductor of electricity and a pair of electrodes sealed at opposite ends of said wall, an outer envelope surrounding said main discharge tube, two outer contacts embedded in said envelope, a gas present in the interspace between said envelope and said main discharge tube, insulated conductors disposed in said interspace for electrically connecting the electrodes of said main discharge tube to said outer contacts, and two bare conductive surfaces disposed opposite each other in said interspace to provide a discharge path which is substantially parallel to that of said electrodes, said surfaces being connected to said outer contacts by said insulated conductors, the gas in said interspace having a pressure adjusted so as to produce a glow discharge between said surfaces when a voltage which is lower than the ignition voltage normally required for said main discharge tube prior to said glow discharge, but sufficient for igniting said main discharge tube during said glow discharge, is applied to said outer contacts.

2. A gas discharge device according to claim 1 wherein the gas in said interspace is a nobel gas with a pressure between 10' Torr and 1 Torr.

3. A gas discharge device according to claim 1, wherein said main discharge tube is a gas and vapor discharge tube.

4. A gas discharge device according to claim 1, wherein said main discharge tube is a vapor discharge tube.

5. A gas discharge device according to claim 1, wherein said bare conductive surfaces are of an electron emissive material.

6. A gas discharge device according to claim 1, wherein said conductive surfaces are connected to said insulated conductor by additional conductor portions including an impedance. 

1. A gas discharge device comprising a main discharge tube having a tubular wall of a material that is a poor conductor of electricity and a pair of electrodes sealed at opposite ends of said wall, an outer envelope surrounding said main discharge tube, two outer contacts embedded in said envelope, a gas present in the interspace between said envelope and said main discharge tube, insulated conductors disposed in said interspace for electrically connecting the electrodes of said main discharge tube to said outer contacts, and two bare conductive surfaces disposed opposite each other in said interspace to provide a discharge path which is substantially parallel to that of said electrodes, said surfaceS being connected to said outer contacts by said insulated conductors, the gas in said interspace having a pressure adjusted so as to produce a glow discharge between said surfaces when a voltage which is lower than the ignition voltage normally required for said main discharge tube prior to said glow discharge, but sufficient for igniting said main discharge tube during said glow discharge, is applied to said outer contacts.
 2. A gas discharge device according to claim 1 wherein the gas in said interspace is a nobel gas with a pressure between 10 3 Torr and 1 Torr.
 3. A gas discharge device according to claim 1, wherein said main discharge tube is a gas and vapor discharge tube.
 4. A gas discharge device according to claim 1, wherein said main discharge tube is a vapor discharge tube.
 5. A gas discharge device according to claim 1, wherein said bare conductive surfaces are of an electron emissive material.
 6. A gas discharge device according to claim 1, wherein said conductive surfaces are connected to said insulated conductor by additional conductor portions including an impedance. 